linux-kernel - Re: [PATCH v2] arm64: dts: qcom: sdm845: Expand soc bus address range

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Date:   Thu, 17 Jan 2019 14:41:16 +0100
From:   Marc Gonzalez <marc.w.gonzalez@...e.fr>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     MSM <linux-arm-msm@...r.kernel.org>,
        DT <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH v2] arm64: dts: qcom: sdm845: Expand soc bus address range

On 16/01/2019 07:49, Bjorn Andersson wrote:

> DMA addresses for devices on the soc bus must be constrained to the 36
> address bits that the bus provides.  When no IOMMU is present then this
> is easy--DMA addresses are just physical addresses and physical
> addresses are (by definition) within the address bits of the bus.  When
> an IOMMU is present, however, DMA addresses are virtual addresses.
> Despite these addresses being virtual, however, they are still
> constrained by the 36 address bits of the bus.
> 
> Unless dma-ranges is specified, which causes bus_dma_mask to be set, DMA
> allocations for devices on the platform_bus will use all 48 address bits
> available by the ARM SMMU. Causing addresses to be truncated on the bus.
> 
> This patch increases the #size-cells to 2, in order to be able to define
> dma-ranges describe the 36 bit DMA capability of the bus, and bumps

Seems like you changed your mind mid-sentence? :-)

> While touching all reg properties, addresses are padded to 8 digits.